One of our toilet cisterns has water hammer which occurs just as the cistern is finishing filling. Also the flush doesn't seem very efficient and the water in the bowl rises quite a bit on flushing. We have checked and there are no blockages. Are these two things related? Would it help to replace the "innards" of the cistern or is this something more complicated? The house is just 4 years old so plumbing is fairly new. Would be most grateful for any help.

Eileen, May 2008

Thanks John. I had the same problem; pipe hammer after cistern had filled. Changed float valve and all fixed now. Cheers.

Ade, January 2009

what has water hammer got to do with a blocked drain ?
shutting stopcocks just reduces the flow not pressure.
a pressure reducing valve does that.
change the float valve or fit a water hammer arrester

sonray heating., May 2008

Hi John. Thanks for your reply. The water hammer is most definitely a hammer. A loud knocking noise just at the end of the filling process. We do have high water pressure and a friend suggested I turn my main stopcock off and then just two turns on, but this did nothing. If I run the wash basin cold tap when the toilet is filling, it does stop the hammer which would suggest the water pressure is high. However, why would this only happen in one toilet and not the other if water pressure is the problem. (Bungalow - two ground level toilets). I don't think scale would be a problem as we live in a very soft water area - no scale on kettles etc.

The manhole for this toilet is right outside the window of the toilet and we have looked at this and in fact we have even removed the toilet to check for blockages and everything is perfectly clear.

I will definitely try your suggestion and change the float valve. Thank you very very much for your reply. If this works, I will come back and let you know.

Eileen, May 2008

Water hammer can take several different forms - either a load banb when a tap or valve is turned off, a vibration in the pipe work or high pitched wine. There are various causes for this such as high water pressure, badly installed pipework or wear/scale build up in taps and valves. As you do not state what sort of a noise is being made, I am guesing the float valve in the cisters either has some wear or scale build up, as in my experience is the most common problem. I would suggest changing this valve in the first instance and see if that solves the problem.
Your second point is the water rising when you flush the toilet. This does suggest a restriction some where in the soil pipe which should be investigated before it becomes a major problem. I would suggest you find the manhole where the toilet runs to, and use a set of drain rods to check for obstructions.
Hope this helps

John, May 2008